Method and system for automatic analysis of particles

ABSTRACT

The present invention relates to a method and a system for automatic analysis of particle size distribution, shape and colour. Sampled particles are distributed into a substantially monolayer particle stream to be exposed to a light source for providing imaging and subsequent analysis of the particles. The samples are collected manually or automatically and placed in containers provided with identification codes which can be read/typed manually or automatically, recorded optically or electronically and the containers are placed in storage devices or sample magazines which can be connected to a sample distribution device for forming the particle stream. The samples can be collected from various process streams and the containers for these samples can be placed in the same storage device for being analysed as a series of analysis. The imaging of the particle stream is performed by camera chosen among several cameras present in the analysing device according to the particle size distribution of the sample. The automatic particle analysing system comprises devices for automatic collection of samples and containers ( 2 ) with identification codes for the samples and storage compartments ( 3 ) for said containers ( 2 ), and the samples can be emptied one by one into a sample distribution device ( 4 ) for forming particle streams suitable for imaging and subsequent analysis. The system comprises several imaging devices being cameras having different types of lenses which can be put automatically into operation as a function of the size of particles to be analysed.

[0001] The present invention relates to a method for automatic analysis to determine particle size distribution, shape and colour and an apparatus for performing the method. The method includes collection of particle samples, transportation of these to means for distributing the particles into a particle stream in the form of a curtain where the particles are substantially distributed in a monolayer to be exposed to a light source for providing an image of the particle curtain to be analysed. The apparatus comprises sample collecting devices, transport means for the samples to a device for distribution of samples into a particle stream suitable for imaging and subsequent analysis.

[0002] The main problem experienced in particle analysis is that commercially available apparatuses and methods only solve separate tasks within the field. Several manual operations are necessary for carrying out the total analysis process and accordingly only part of the process will in practice be automatic. In most cases only separate samples can be analysed at a time and new samples have to be collected, prepared, marked/registered and formed into suitable particle streams for imaging and subsequent computerized analysis/treatment of the images. The result of said problems is that it is quite time-consuming to perform analysis of particle samples, and indeed of series of samples from different production streams of a plant.

[0003] Several apparatuses and measuring/analysing techniques related to particle analysis are known in the art. Thus a particle analysis apparatus where a silhouette projection method is used, is described in U.S. Pat. No. 4,497,576. The apparatus includes use of parallel laser beams directed through a sample of particles, and means for recording the light which has passed through. This recording is then analysed to reveal the particle size distribution of the sample. The particles to be analysed are transported on a conveyor belt and fall from it in front of a light source and down to a next belt to be returned to the process. The particles falling from the belt shall form a monolayer of particles and they shall fall at the same speed. How this can be achieved is not explained. Analysis of particle size distribution is also known from EP-0348469 B1, which describes a method and means creating a monolayer curtain of particles to be analysed. The particles are fed manually via a silo onto a vibrating plate being at such a distance from the silo outlet that the uppermost layer of said particles on said plate forms an angle a with the horizontal plane which is 95%-50% of the sliding angle of said particles. Though a reliable monolayer is provided with this method and means, they are restricted to analysing single samples, one at a time. The imaging of the particle curtain has to be finalized before a new sample of particles can be fed to the apparatus for being formed into a monolayer of particles. Imaging and analysing of a particle stream is also known from GB-2,333,594 A which describes an apparatus comprising electrooptical scanning of the particle stream with an optoelectronic measurement section formed by a light source and an image collecting device. The image collecting device comprises a plurality of electrooptical image recording units aligned onto the particle stream, said units having different image scales which are mutually matched to cover the overall measurement range of the apparatus. This way of covering the overall measurement range avoids the manual work of changing lenses and camera position, but it is also restricted to performing analysis of single samples, and there are not shown special provisions for securing a monolayer of particles to be imaged.

[0004] In U.S. Pat. No. 4,295,200 there is described an automatic particle analysing system comprising supply of several samples to a particle distributor. Sample cups filled with particles are fixed on to a conveyer belt which can pass over a particle distribution device. A measured stream of particles is dropped onto the apex of a distribution cone when a cup passes over the cone. The particles are then divided into a circular pattern falling through a narrow sizing zone onto the spherical edge of a rotable platen. By this means the particles can be analysed one-by-one as each particle is carried into a frame area viewed, preferably by a microscope and a TV camera, the output of which is applied to a computer programmed to analyse selected characteristics. This system makes it possible to analyse each particle in a sample, and can continue on the next sample when the last particle of the first sample is analysed. But such a device is very sensitive to the particle size distribution before imaging, as large particles will get stuck in the narrow sizing zone of the apparatus. Another limitation of the capacity of the system is that the particles have to be analysed one-by-one, and the practical use of this system will be restricted to laboratories as it will not be applicable for analysing particles in a continuous industrial process.

[0005] The main object of the present invention was to arrive at a versatile and automatic method and apparatus for analysis of a plurality of samples of particles and being applicable both for on-line analysis and laboratory analysis.

[0006] Another object was to combine sample collection from various process streams with supply of these to a single particle analysing apparatus without applying any manual work and still be able to keep track of the origin of the samples with regard to time and place for collection of the various samples.

[0007] A further object was to be able to perform sequential analysis of samples, for instance analysis of samples taken at the same time from various process streams.

[0008] It was also an object to develop a method that could cover a wide range of particle size distribution, shape and colour.

[0009] In spite of the fact that numerous methods and apparatuses for particle analysis are on the market, the inventors found that none of these or combinations of them could meet their demand for a versatile and robust system. A thorough investigation of advantages and disadvantages of known methods revealed that further developments were necessary for reducing the manual work in connection with particle analysis. It was also found that quality control of such systems needed to be improved. The inventors first looked into each manual operation in order to evaluate the possibility for automation and improvement of the operation. It was then found that the sampling should be combined with placement of the sampled particles in containers which could be transported to the central unit of a particle analyser. This conclusion then led to the problem of identifying the samples later on. This problem was simply solved by providing each container with identification codes (ID) which could be arranged for sample sequency in the magazine and the analyser is set up for analysing the samples according to the sequence of the samples and/or read for recording by conventional optical/electronical registration devices. It would then be possible to identify the samples throughout the whole process with regard to time and place for the sampling and also other informations of interest such as temperature, humidity etc. at the time of sampling. In some cases it would also be of interest to treat the samples before analyses. Such treatment, comprising drying, dividing, crushing, sieving etc., should then be performed before the sample was put into the container. In connection with particle analysis it would in some cases be an advantage if the analysis could be performed in sequences or series, for instance performing analysis in series of samples taken at the same time from different process streams. The inventors then found that this could be achieved by applying the concept of sample containers having ID's. Desired sample series could be collected into one storage device supplied to the central analysing apparatus. In other cases several samples from one sample collection site could be stored in said storage device for transport to the analyser. By the above arrangement any desired series of samples could be fed to the analyser, where separate samples from the storage device could be transformed into a stream of particles having a suitable form for being imaged and analysed. The particle stream should preferably constitute a monolayer of particles, and this can be achieved by known means such as vibrating plates to which the sample is fed. Further it was found that even the imaging part could be improved by providing several image recording devices such as cameras in the analyser. The cameras could have different size/type of lenses and depending on the type of samples and size of particles to be analysed, the appropriate camera or cameras could be put into operation. As the system comprises computer programs for automatic selection of camera or cameras and for automatic collection of samples and even placement of these into desired storage compartments, the results from the analyser can be used to trigger samples and types of samples to be analysed next. The analysis can of course also be used as feedback to a process. The system is advantageously equipped with various types of alarms which are triggered when the analysis shows predetermined deviations from desired values.

[0010] The main feature of the method according to the invention is that the samples are collected manually or automatically and placed in containers provided, as known per se, with identification codes which can be read/typed manually or automatically, recorded optically or electronically and that the containers are placed in storage devices or sample magazines which can be connected to a sample distribution device for forming particle stream suitable for imaging and subsequent analysis and the imaging of the particle stream is performed by camera chosen among several cameras present in the analysing device according to the particle size distribution of the sample.

[0011] Prior to placement in containers the samples can be subjected to treatment like drying, dividing, crushing or sieving.

[0012] The samples can be collected from various process streams, and the containers for these samples can be placed in the same storage device for being analysed as a series of analysis.

[0013] The results of the analysis can trigger feedback or alarm if the results deviate from pre-defined values and said feedback can be conveyed to the control system of the process.

[0014] The containers can be provided with samples sequency in the magazine, and the analyser can be set up for analysing the samples according to the sequency of the samples.

[0015] The sample containers can contain samples with a wide range of particle size distributions, shape and colour.

[0016] The main features of the automatic particle analysing system according to the invention comprise devices for automatic collection of samples and containers 2 with identification codes for the samples and storage compartments 3 for said containers 2. The samples can be emptied one by one into a sample distribution device 4 for forming particle streams suitable for imaging by camera which can be chosen among several cameras present in the analysing device and subsequent analysis.

[0017] The system can comprise several imaging devices being cameras having different types of lenses which can be put automatically into operation as a function of the size of particles to be analysed.

[0018] The system can comprise several compartments for sample containers and there can be provisions for transportation of said compartments to the sample distribution device.

[0019] The invention is further explained in connection with the FIGURE.

[0020]FIG. 1 shows the central units of a particle analysis system according to the invention.

[0021] In FIG. 1 there is shown a particle analysing apparatus 1 comprising imaging devices such as at least one camera and a light source for lightening the stream of particles delivered from the vibrating chute 4 into the apparatus 1. Having been analysed, the particles are collected and removed from the apparatus 1 through the drawer 7. A conveyor belt can also be used for removing the analysed particles and if desired returned to the process from which they were collected. The samples of particles are transported from the sampling site to the central unit in containers 2. These can then be fed to the chute 5 and further into a rotatable storage compartment 3. The containers 2 can also be loaded into compartment 3, which then are connected to the central analysing unit. When the compartment 3 rotates, the containers 2 are emptied down on a vibrating chute 4. The particles leave the chute 4 in a stream which is substantially a monolayer of particles. Emptied containers 2 leave the central unit through chute 6 and are then transported back to the process for being refilled with samples of particles to be analysed.

[0022] By applying the method according to the invention and automatic analysing system as shown in FIG. 1, the inventors have succeeded in solving the main problems related to known methods and systems in the field. A versatile, robust and high capacity method and system have been achieved by the invention. Manual labour has been minimized and the quality control and reliability of the particle analysis have been substantially increased as a results of applying sample containers with ID's. 

1. Method for automatic analysis of particle size distribution, shape and colour, comprising collection of particle samples, transportation of these to means for distributing the particles into particle streams, where the particles are distributed into a substantially monolayer particle stream to be exposed to a light source for providing imaging and subsequent analysis of the particles, characterized in that the samples are collected manually or automatically and placed in containers provided, as known per se, with identification codes which can be read/typed manually or automatically, recorded optically or electronically and that the containers are placed in storage devices or sample magazines which can be connected to a sample distribution device for forming particle stream suitable for imaging and subsequent analysis and that the imaging of the particle stream is performed by camera chosen among several cameras present in the analysing device according to the particle size distribution of the sample.
 2. Method according to claim 1, characterized in that the samples prior to placement in containers are subjected to treatment like drying, dividing, crushing or sieving.
 3. Method according to claim 1, characterized in that samples are collected from various process streams and that the containers for these samples are placed in the same storage device for being analysed as a series of analysis.
 4. Method according to claim 1, characterized in that the results of the analysis triggers feedback or alarm if the results deviate from pre-defined values and that said feedback is conveyed to the control system of the process.
 5. Method according to claim 1, characterized in that the containers are provided with samples sequency in the magazine and that the analyser is set up for analysing the samples according to the sequency of the samples.
 6. Method according to claim 1, characterized in that the sample containers contain samples with a wide range of particle size distributions, shape and colour.
 7. Automatic particle analysing system comprising sampling means, transportation means for the samples to a device for distributing the sample into a particle stream suitable for imaging and subsequent analysis, characterized in that the system comprises devices for automatic collection of samples and containers (2) with identification codes for the samples and storage compartments (3) for said containers (2), and where the samples can be emptied one by one into a sample distribution device (4) for forming particle streams suitable for imaging by camera which can be chosen among several cameras present in the analysing device and subsequent analysis.
 8. Automatic system according to claim 8, characterized in that the system comprises several imaging devices being cameras having different types of lenses and which can be put automatically into operation as a function of the size of particles to be analysed.
 9. Automatic system according to claim 8, characterized in that the system comprises several compartments for sample containers and that there are provisions for transportation of said compartments to the sample distribution device. 